package com.hzncc.scaffold.utils;

import org.springframework.lang.NonNull;

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * 线程池的工具类
 * 用于进行线程的管理，防止重复创建、杀死线程。
 * <p>
 * 多线程运行期间，如果系统不断的创建、杀死新线程，
 * 会产生过度消耗系统资源，以及过度切换线程的问题，甚至可能导致系统资源的崩溃。
 * 因此需要线程池，对线程进行管理。
 */
public class ThreadPoolUtil {

  private static volatile ThreadPoolUtil mInstance;
  private String TAG = getClass().getName();
  //核心线程池的数量，同时能够执行的线程数量
  private int corePoolSize;
  //最大线程池数量，表示当缓冲队列满的时候能继续容纳的等待任务的数量
  private int maxPoolSize;
  //存活时间
  private long keepAliveTime = 1;
  private TimeUnit unit = TimeUnit.HOURS;
  private ThreadPoolExecutor executor;

  private ThreadPoolUtil() {
    //给corePoolSize赋值：当前设备可用处理器核心数*2 + 1,能够让cpu的效率得到最大程度执行（有研究论证的）
    corePoolSize = Runtime.getRuntime().availableProcessors() * 2 + 1;
    maxPoolSize = corePoolSize;
    executor = new ThreadPoolExecutor(
        //当某个核心任务执行完毕，会依次从缓冲队列中取出等待任务
        corePoolSize,
        // 然后new LinkedBlockingQueue<Runnable>(),然后maximumPoolSize,但是它的数量是包含了corePoolSize的
        maxPoolSize,
        //表示的是maximumPoolSize当中等待任务的存活时间
        keepAliveTime,
        unit,
        //缓冲队列，用于存放等待任务，Linked的先进先出
        new LinkedBlockingQueue<>(),
        new DefaultThreadFactory(Thread.NORM_PRIORITY, "thread-pool-"),
        new ThreadPoolExecutor.AbortPolicy()
    );
  }

  public static ThreadPoolUtil getInstance() {
    if (mInstance == null) {
      synchronized (ThreadPoolUtil.class) {
        if (mInstance == null) {
          mInstance = new ThreadPoolUtil();
        }
      }
    }
    return mInstance;
  }

  /**
   * 执行任务
   *
   * @param runnable
   */
  public void execute(Runnable runnable) {
    if (executor == null) {
      executor = new ThreadPoolExecutor(
          corePoolSize,
          maxPoolSize,
          keepAliveTime,
          TimeUnit.SECONDS,
          new LinkedBlockingQueue<>(),
          new DefaultThreadFactory(Thread.NORM_PRIORITY, "thread-pool-"),
          new ThreadPoolExecutor.AbortPolicy());
    }
    if (runnable != null) {
      executor.execute(runnable);
    }
  }

  /**
   * 移除任务
   *
   * @param runnable
   */
  public void remove(Runnable runnable) {
    if (runnable != null) {
      executor.remove(runnable);
    }
  }

  private static class DefaultThreadFactory implements ThreadFactory {

    //线程池的计数
    private static final AtomicInteger poolNumber = new AtomicInteger(1);
    //线程的计数
    private final AtomicInteger threadNumber = new AtomicInteger(1);
    private final ThreadGroup group;
    private final String namePrefix;
    private final int threadPriority;

    DefaultThreadFactory(int threadPriority, String threadNamePrefix) {
      this.threadPriority = threadPriority;
      this.group = Thread.currentThread().getThreadGroup();
      this.namePrefix = threadNamePrefix + poolNumber.getAndIncrement() + "-thread-";
    }

    @Override
    public Thread newThread(@NonNull Runnable r) {
      Thread thread = new Thread(group, r, namePrefix + threadNumber.getAndIncrement(), 0);
      // 返回True该线程就是守护线程
      // 守护线程应该永远不去访问固有资源，如：数据库、文件等。因为它会在任何时候甚至在一个操作的中间发生中断。
      if (thread.isDaemon()) {
        thread.setDaemon(false);
      }
      thread.setPriority(threadPriority);
      return thread;
    }
  }
}